Self-quenching electrode for crossed field traveling wave devices

ABSTRACT

A crossed field device of the reentrant electron beam and nonreentrant nonresonant transmission network type having means for substantially automatically quenching electron-traveling wave interaction initiated by electromagnetic energy signal pulses during nonoperation intervals. Such means are disposed adjacent to the drift space area of the interaction region and include a lumped capacitive-resistive network coupled to electrode means to rapidly terminate electron emission.

United States Patent Inventor Edward C. Dench Annisquam, Mass.

Appl. No. 880,580

Filed Nov. 28, I969 Patented May 4, 1971 Assignee Raytheon Company Lexington, Mass.

SELF-QUENCHING ELECTRODE FOR CROSSED FIELD TRAVELING WAVE DEVICES [56] References Cited UNITED STATES PATENTS 2,633,505 3/1953 Lerbs 330/43 2,676,246 4/1954 Rinia 330/43X 3,096,457 7/1963 Smith, Jr. et a1. 315/39.3X 3,255,422 6/1966 Feinstein et a1 315/39.3X

Primary ExaminerHerman Karl Saalbach Assistant Examiner-Saxfield Chatmon, Jr.

Attorneys-Harold A. Murphy, Joseph D. Pannone and Edgar O. Rost ABSTRACT: A crossed field device of the reentrant electron beam and nonreentrant nonresonant transmission network type having means for substantially automatically quenching electron-traveling wave interaction initiated by electromagnetic energy signal pulses during nonoperation intervals. Such means are disposed adjacent to the drift space area of the interaction region and include a lumped capacitive-resistive network coupled to electrode means to rapidly terminate electron emission.

11 Claims, 4 Drawing Figs.

US. Cl 3l5/39.3, 330/43, 331/82, 315/35 Int.C1 H0lj 25/34 Field of Search 315/35 (X), 3.6 (X); 330/41, 43; 315/393, 3.5, 3.6; 331/82 RF SIGNAL OUTPUT PATENTED HAY 41971 SHEET 1 BF 2 x l w 3/ 1 7 v a v m mm m a 2 m #1. M F

RF SIGNAL OUTPUT RFSIGNIAL RF SIGNAL, OUTPUT INPUT FIG? INVENTOR EDWARD 6. BENCH ATTORNEY PATENTED MAY 4 Ian sum 2 07 2 RFSIGNAL INPUT RF SIGNAL our u7 RF SIGNAL INPUT RF SIGNAL OUTPUT x/vvav rok EDWARD c. DEA/CH 71 ATTORNEY SELF-QUENCHING ELECTRODE FOR CROSSED FIELD TRAVELING WAVE DEVICES BACKGROUND OF THE INVENTION Crossed field devices of the type under consideration commonly are provided with an axially disposed continuously coated cold cathode. Secondary electron emission is initiated by an injected electromagnetic energy signal pulse applied to a nonreentrant signal transmission network hereinafter also referred to as the anode circuit terminating at its,ends in external input and output coupling means separated by a gap referred to as the drift space." A static DC magnetic field is conventionally disposed parallel to the axis of the cathode and an electric potential is applied between the cathode and anode circuit. An interacting electron stream is formed having velocities determined by the ratio of the electric to the magnetic field. Spokes of rotating space charge are thus formed. The direction of beam rotation relative to wave energy on the anode circuit and the input and output coupling means determines the operating characteristics of the device. For forward wave interaction the wave energy to be amplified is injected at one-set of input terminals of the anode circuit and flows in a similar direction as the beam with the phase velocity of said waves being substantially synchronous with the stream velocity to thereby cause energy to be delivered to the waves and result in a growing wave with distance. Propagation of the wave energy in a counterclockwisedirection to the reentrant electron beam results with reversal of the input and output ter- :minal connections and a fundamental backward wave device will result. In either device energy may be amplified or generated. After the triggering of the cold cathode emission and anode circuit current by an incoming pulse, particularly, in'the case of a crossed field amplifier, the termination of such -a pulse has generally been ineffective in quenching the electron emission. As a result, undesirable continuation of the electron-wave interaction will occurin the fundamental operation mode.

a In the prior art, several suggestions for remedying this disadvantage of cold cathode crossed field devices have been noted. One such means includes reducing the interpulse anode to cathode potential by appropriate auxiliary circuits in the power supply to the threshold point at which interaction ceases. This method, however, is costly in view of the requirement for rather complex pulse modulators for the anodecathode power supply.

Alternatively, modifications in the cathode structure to provide insulated tumofi' electrode segments or the provision of auxiliary or gridded electrodes within the device with accompanying separate potential sources have been utilized. In such structures the application of a negative potential to reduce the anode-cathode field or a positive potential to collect the electron beam will provide for collapse of secondary electron emission. Additional voltage sources as well as modification of the power supplies 'are, however, always complicated and costly.

It is desirable, therefore, to provide a simple and inexpensive method as well as means for quenching of secondary electron emission in cold cathode devices, particularly, of the crossed field configuration. The electron quenching may be desired either during the period of the incoming electromagnetic energy signal pulse or shortly after the termination of such a pulse.

SUMMARY OF THE INVENTION In accordance with the teachings of the present invention a traveling wave crosed field amplifier or oscillator is provided having interpulse electron beam-quenching means without sistive network having a predetermined value is included with the capacitive component adapted to charge when the device is operative after initiation of cold cathode secondary electron emission. During the cathode electron emission cycle, current flows in the anode circuit. A portion of this current is collected on the auxiliary electrode by reason of the voltage developed across the resistor causing the capacitive component to charge. The electric field thereby varies causing a decrease in the potential difference between the electrode and cathode in the drift space. The reentrant electron beam is thereby substantially decelerated to the point where secondary electron emission is markedly quenched or ceases. At this time interval the initial electromagnetic energy trigger pulse has terminated and the capacitive component is discharged to ground. The crossed field device returns to the quiescent or nonoperative condition until the next pulse is received at which time the charging and discharging cycles are repeated.

In another embodiment the cold cathode member is modified to provide an isolated segment adjacent to the drift space defining an auxiliary secondary emissive cathode electrode. Capacitive-resistive components are connected between the branch of the DC power supply coupled to the main and auxiliary cathode electrodes. Up'on initiation of emission the auxiliary cathode electrode assumes a more positive potential with respect to the remaining cathode portions. The voltage and electric field in the drift space area is thereby reduced to the point of self-quenching of thebeam to return the device to its quiescent state.

In still another embodiment a predetermined degree of regulation is provided in either the cathode or anode branch of the DC power supply. Once the cathode becomes emissive in response to an incoming signal pulse, a voltage is developed across the resistance and the total electric field between the cathode and anode is reduced to a point where secondary emission is quenched. The tube reverts to its quiescent condition until the next pulse is received.

Numerous variations of the foregoing embodiments are taught in the ensuing description and forward as well as backward wave configurations may be practiced.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, as well as the details for the provision of preferred embodiments, will be readily understood after consideration of the following detailed description and reference to the accompanying drawings, wherein:

FIG. 1 is a diagrammatic presentation illustrative of the embodiment of the invention incorporating current reduction means in the anode circuit branch; 5

FIG. 2 is a schematic diagram of another embodiment incorporating the invention in the cathode circuit branch;

FIG. 3 is a schematic diagram of still another alternative embodiment of the invention;

and FIG. 4 is a schematic diagram of a further embodiment of the invention incorporating a capacitive-resistive network between the anode and cathode circuit branches of the DC supply.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to the drawings, particularly FIG. 1, an illustrative embodiment of the invention is shown relating to a crossed field amplifier device 2. A nonreentrant type slow wave electromagnetic energy propagating line comprises the anode circuit 4 which has been illustrated diagrammatically for the sake of clarity. In view of the fact that the invention encompasses all types of traveling wave devices having a nonreentrant anode circuit such energy propagating means as interdigital delay lines including rod or vane members, meander lines as well as ladder lines may be employed. The anode members can be alternately strap loaded and the device operates substantially as a saturated amplifier or locked oscillator. A fuller and more complete analysis as well as description of the applicable devices together with anode circuits may be had by referring to the text "Crossed Field Devices E. Okress et al., Vol. l, Academic Press, New York, N.Y., pps. 11-15, 47- 67, as well as US. Pat. No. 2,681,427 issued June 15, 1954 to W.C. Brown et al., US Pat. No. 2,859,411 issued Nov. 4,

1958 to W.C. Brown and U.S. Pat. No. 3,255,422 issued June 7, l966'to .l. Feinstein et al.

The anode circuit is provided with a gap 6 identified as the drift space adjacent to its terminal ends. Signal input means 8 are attached to one tenninal member component of the anode circuit and signal output means 10 are connected to another of the anode circuit terminal members. The input and output ends of the anode circuit are isolated from one another. Concentrically disposed within the area defined by the anode circuit is an axially disposed continuous cathode member 12. lllustratively, in such crossed field devices, the cathode is of the nonthermionic-type adapted to copiously emit secondary electrons upon bombardment by a source of primary electrons such as an initiating pulse coupled from an RF input line. The cathode member is, therefore, desirably fabricated of any of the well-known materials having a secondary electron emission ratio greater than unity such as platinum, beryllium-beryllium oxide or aluminum-aluminum oxide. The electrons traverse the interaction region 14 defined between the anode and cathode circuits with rotation of the electron space charge in a clockwise direction indicated by the arrow 16. The electron stream velocity is determined by an electric field established between the anode and cathode and a mutually perpendicular magnetic field parallel to the cathode axis as indicated by the circle 18. A DC power supply of, illustratively, 20 Kilovolts biases the anode-cathode circuit in a cold cathode crossed field-type device.

An incoming electromagnetic energy signal wave on input 8 will be propagated at a phase velocity determined by the anode circuit. Resultant electron beam-wave interaction is established when a substantially synchronous relationship exists with the fundamental forward wave component which is circulated in substantially a clockwise manner. Reversal, of course, of the input and output terminals will provide for a backward wave mode interaction device.

In accordance with one proposed method of incorporating the teachings of the invention in such devices an auxiliary electrode 22 is disposed in the anode circuit adjacent to the drift space area of the overall interaction region and forms a continuation of and has essentially the same contour configuration as the anode circuit. The electrode 22 is biased electrically by a line 24 with a resistor element 26 serially connecting this circuit to the positive side of the DC power supply 20. A capacitive component 28 is tied in parallel across the branch line 24 and another line 30. The remaining capacitive component 32 is intended to diagrammatically represent all the inherent capacitances within the device since the anode circuit network commonly provides a large capacitance value between its respective members.

With the foregoing circuit, the operation of the device will now be described. Without a trigger pulse on the inputline, the device is considered to be in the quiescent state with no cathode emission and no current drawn from the DC power supply. When an input RF signal is propagated along the anode circuit, electrons are caused to.be emitted from the cold cathode. Current flows in the anode circuit and an amplified signal will emanate from the output means 10. In the operative state a portion of the anode current will be collected on the auxiliary electrode 22 thereby causing the capacitive component 28 to store energy. 1 A resultant potential difference in the electric field established between the auxiliary electrode 22 and the opposing cathode 12 tends to decrease in the drift space area 6. Upon a sufficient decrease in the electric field potential established in this area the secondary electron emission is reduced and the reentrant electron beam is decelerated. By means of the time transient circuit, then, the varying of the electric field potential results in a threshold value incapable of further electron emission. The electron beam by means of the incorporation of this circuit thereby becomes substantially self-quenching until another initiating pulse of sufficient amplitude is injected along the input line. When the initiating pulse signal terminates, the auxiliary elec trode 22 will be at anode potential through the serially con nected resistor element 26. The capacitor element 28, which is mounted across the resistor will then discharge and the device is rapidly returned to the quiescent state during the interpulse period. By this means a crossed field device has been provided of the cold cathode type which provides for electron beam quenching during the interpulse periods.

Referring next to FIG. 2 an alternative means for achieving the self-quenching feature is disclosed. ln this embodiment a secondary-emitting auxiliary cathode segment 34 is provided having substantially the same contour as the remaining cathode segment 36. The auxiliary capacitive-resistive network 38 is then coupled between the negative branch 40 of the power supply 20 and the aforementioned cathode segment 34. Network 38 includes the inherent capacitance 42 of the cathode segment 34 and its lead 40. Additionally, a capacitance 44 is now provided externally or internally in parallel with capacitance 42. The resistor 46 in series completes the network 38 and has a value sufficient to tie this component in with the main cathode circuit and initiate secondary emission. The anode circuit 4 is circumferentially disposed about the segmented cathode and this circuit as well as other components previously illustrated in FIG. 1 have been similarly numbered. For the purposes of the illustration the anode circuit is electrically continuous biaswise, as indicated by the line 48. Since the energy propagation path is nonreentrant, the input means 8 and output means 10 are isolated. Space 50 is shown to represent diagrammatically that electromagnetic energywise the anode members are mutually isolated. lt will be noted that the cathode self-quenching means 34 is again disposed in close proximity to the drift space area In operation the cathode-anode electric field is reduced in the drift space area after initiation of secondary emission by an external signal pulse with the auxiliary electrode segment 34 assuming a more positive potential with respect to the remainder of the cathode structure. Such a positive potential tends to decrease the voltages and electric field between the anode and cathode circuit to the point that the electron beam trajectory collapses and the tube returns to the quiescent state. In this embodiment the capacitance is again discharged at substantially the time interval when the RF pulse has terminated.

Referring now to FIG. 3, still another embodiment of the invention is diagrammatically illustrated. Similar structure heretofore described has been similarly numbered. ln this embodiment the capacitive-resistive circuit may now be provided.

in one of the branches of the DC power supply 20 serving the anode or cathode circuits. It will be noted that in this configuration no auxiliary electrode means are utilized. The cathode branch 52 incorporates the auxiliary network 54 including capacitor 56 and resistor 58 in addition to the inherent capacitance designated by the numeral 60. Once the tube becomes operative a voltage is developed across the resistor 58 and the capacitor 56 charges. The total capacitance 56 and 60 are then broughtto a predetermined value causing the potential difference between the anode and cathode to drop below the level necessaryfor a self-sustaining secondary electron emission state. The space charge current thereby collapses and the capacitor discharges through the resistor to ground until the initial quiescent condition is restored. The device remains in the quiescent state until the initiating pulse is again received to commence the emission-charging cycle. Auxiliary circuit 54 may also be incorporated in the line 62 for the anode circuit between the points 64 and 66 with comparable results.

A final embodiment is disclosed in FIG. 4. The power supply 20 biases the anode-cathode circuit by serially connected resistor 68. The inherent tube capacitance 70 is in parallel between the lines 72 and 74 and the additional capacitance in the circuit is disposed in parallel across the power supply by means of additional capacitance 76; This circuit will operate in essentially the same manner as the previously described embodiments. In this embodiment the separation of the input and output coupling means of the nonreentrant anode circuit are assumed to be an inherent feature of the structure of the tube and has, therefore, not been specifically illustrated.

a in all of the foregoing embodiments the values for the capacitive-resistive network may be empirically determined and will be dependent upon such parameters as the DC voltage potentials, tube dimensions, magnetic fields, as well as frequency band of operation. An additional modification which may be practiced in accordance with the teachings of the invention involves the provision of a secondary emissive cathode structure in the area of the cathode space having a lower effective emission ratio to further improve the selfquenching features of the invention. In the practice of the above-described invention overall improvement in the operation of the tube efficiency should be realized since the electron collection in the region of the drift space is effectively inhibited by the reduced electric fields provided through the capacitor and resistor components in the auxiliary network. It is realized that numerous other arrangements as well as modifications may be evident to those skilled in the art without deviating from the spirit and scope of the invention as defined in the appended claims. It is intended, therefore, that the foregoing description be considered as exemplary only and not in a limiting sense.

lclaim:

I. A traveling wave device comprising:

a source of electrons;

means including electrodes and an applied electric field for initiating emission of a beam of electrons and operation of said device in response to an input electromagnetic energy radio frequency signal;

and means comprising a capacitive-resistive electrical network coupled to the electric field-producing means for terminating operation of the device responsive to a change of the electric field potential of the electrode means resulting from operation of the device.

2. A traveling wave device comprising:

a source of electrons;

means including electrodes and an applied electric field for initiating emission of a beam of electrons and operation of said device in response to an input electromagnetic energy radio frequency signal;

and means comprising a capacitive-resistive electrical network coupled to the electric field-producing means for terminating operation of the device responsive to removal of said input signal and a change of the electric field potential of the electrode means resulting from operation of the device.

3. A traveling wavedevice comprising:

a secondary electron emissive cathode adapted to emit an electron beam in a substantially reentrant path;

means including electrodes and an applied electric field for initiating electron emission and operation of the device in response to an input electromagnetic energy radiofrequency signal; 1

and means comprising a capacitive-resistive electrical network coupled to the electric field-producing meansfor terminating operation of the device by a change of the electric field potential of the electrode means in a portion of said beam reentrant path as a result of the operation of the device.

4. A traveling wave device comprising:

a nonreentrant electromagnetic energy-propagating structure having at least two terminations and defining therebetween a gap;

input signal means coupled to one of said temtinations;

a secondary electron emissive cathode adapted to emit an electron beam in a substantially reentrant path;

means including said propagating structure and cathode together with an applied electric field for initiating electron emission to operate said device in response to an input electromagnetic energy radiofrequency signal;

and means comprising a capacitive-resistive electrical network coupled to the electric field-producing means for terminating operation of the device by a change of the electric field potential in the gap as a result of the operation of the device to substantially quench the electron beam after cessation of said input signal.

S. A traveling wave device comprising:

a nonreentrant electromagnetic energy-propagating structure having at least two terminations and defining therebetween a gap;

input signal means coupled to one of said terminations; a secondary electron emissive cathode adapted to emit an electron beam in a substantially reentrant path in energy exchanging relationship with energy propagating on said structure; 1

an auxiliary electrode disposed in said gap;

means for applying an electric field along said reentrant path and initiating electron emission in response to an input electromagnetic energy radiofrequency signal;

and means comprising a capacitive-resistive electrical network coupled to the electric field-producing means for terminating operation of the device by a change of the electric field potential between the auxiliary electrode and cathode as a result of operation of the device to substantially quench the electron beam after cessation of said input signal.

6. A traveling wave device comprising:

a nonreentrant electromagnetic energy-propagating structure having at least two terminations and defining therebetween a gap;

input signal means coupled to one of said terminations;

a secondary electron emissive cathode having at least two segments adapted to emit an electron beam in a substantially reentrant path;

means for applying an electric field along said reentrant path and initiating electron emission in response to an input electromagnetic energy radiofrequency signal;

and means comprising a capacitive-resistive electrical network coupled to the electric field-producing means for terminating operation of the device by a change in the electric field potential in said path adjacent to one of said cathode segments as a result of operation of the device to substantially quench the electron beam after cessation of said input signal. 1

7. A traveling wave device according to claim 6 wherein one of said cathode segments is disposed adjacent to said gap.

8. A traveling wave device according to claim 6 wherein one of said cathode segments has a lower secondary electron emission characteristic than the remainder of said cathode.

9. A crossed field electron discharge device comprising:

means for propagatingelectromagnetic energy along a nonreentrant path;

mutually isolated input and output means coupled to the tenninal ends of said propagating means and defining therebetween a drift space area;

means for generating and directing a reentrant beam of electrons adjacent to said path and defining with said propagation means a continuous interaction region of substantially uniform configuration;

means for producing mutually perpendicular electric and magnetic fields in said interaction region;

and means for varying the electric fields in said drift space area comprising a capacitive-resistive electrical network coupled to the electric field-producing means to provide for a reduction of the electric field potential at a predetermined time interval to thereby substantially terminate the electron beam generation.

10. A crossed field device according to claim 9 wherein a resistive component is coupled in series with said-electric field-producing means and a capacitive component is coupled in parallel with said electric field-producing means.

11. A crossed field device according to claim 9 wherein said 

1. A traveling wave device comprising: a source of electrons; means including electrodes and an applied electric field for initiating emission of a beam of electrons and operation of said device in response to an input electromagnetic energy radio frequency signal; and means comprising a capacitive-resistive electrical network coupled to the electric field-producing means for terminating operation of the device responsive to a change of the electric field potential of the electrode means resulting from operaTion of the device.
 2. A traveling wave device comprising: a source of electrons; means including electrodes and an applied electric field for initiating emission of a beam of electrons and operation of said device in response to an input electromagnetic energy radio frequency signal; and means comprising a capacitive-resistive electrical network coupled to the electric field-producing means for terminating operation of the device responsive to removal of said input signal and a change of the electric field potential of the electrode means resulting from operation of the device.
 3. A traveling wave device comprising: a secondary electron emissive cathode adapted to emit an electron beam in a substantially reentrant path; means including electrodes and an applied electric field for initiating electron emission and operation of the device in response to an input electromagnetic energy radiofrequency signal; and means comprising a capacitive-resistive electrical network coupled to the electric field-producing means for terminating operation of the device by a change of the electric field potential of the electrode means in a portion of said beam reentrant path as a result of the operation of the device.
 4. A traveling wave device comprising: a nonreentrant electromagnetic energy-propagating structure having at least two terminations and defining therebetween a gap; input signal means coupled to one of said terminations; a secondary electron emissive cathode adapted to emit an electron beam in a substantially reentrant path; means including said propagating structure and cathode together with an applied electric field for initiating electron emission to operate said device in response to an input electromagnetic energy radiofrequency signal; and means comprising a capacitive-resistive electrical network coupled to the electric field-producing means for terminating operation of the device by a change of the electric field potential in the gap as a result of the operation of the device to substantially quench the electron beam after cessation of said input signal.
 5. A traveling wave device comprising: a nonreentrant electromagnetic energy-propagating structure having at least two terminations and defining therebetween a gap; input signal means coupled to one of said terminations; a secondary electron emissive cathode adapted to emit an electron beam in a substantially reentrant path in energy exchanging relationship with energy propagating on said structure; an auxiliary electrode disposed in said gap; means for applying an electric field along said reentrant path and initiating electron emission in response to an input electromagnetic energy radiofrequency signal; and means comprising a capacitive-resistive electrical network coupled to the electric field-producing means for terminating operation of the device by a change of the electric field potential between the auxiliary electrode and cathode as a result of operation of the device to substantially quench the electron beam after cessation of said input signal.
 6. A traveling wave device comprising: a nonreentrant electromagnetic energy-propagating structure having at least two terminations and defining therebetween a gap; input signal means coupled to one of said terminations; a secondary electron emissive cathode having at least two segments adapted to emit an electron beam in a substantially reentrant path; means for applying an electric field along said reentrant path and initiating electron emission in response to an input electromagnetic energy radiofrequency signal; and means comprising a capacitive-resistive electrical network coupled to the electric field-producing means for terminating operation of the device by a change in the electric field potential in said path adjacent to one of said cathode segments as a result of operation of the device to substantially quench the electron beam after cessatioN of said input signal.
 7. A traveling wave device according to claim 6 wherein one of said cathode segments is disposed adjacent to said gap.
 8. A traveling wave device according to claim 6 wherein one of said cathode segments has a lower secondary electron emission characteristic than the remainder of said cathode.
 9. A crossed field electron discharge device comprising: means for propagating electromagnetic energy along a nonreentrant path; mutually isolated input and output means coupled to the terminal ends of said propagating means and defining therebetween a drift space area; means for generating and directing a reentrant beam of electrons adjacent to said path and defining with said propagation means a continuous interaction region of substantially uniform configuration; means for producing mutually perpendicular electric and magnetic fields in said interaction region; and means for varying the electric fields in said drift space area comprising a capacitive-resistive electrical network coupled to the electric field-producing means to provide for a reduction of the electric field potential at a predetermined time interval to thereby substantially terminate the electron beam generation.
 10. A crossed field device according to claim 9 wherein a resistive component is coupled in series with said electric field-producing means and a capacitive component is coupled in parallel with said electric field-producing means.
 11. A crossed field device according to claim 9 wherein said capacitive component is adapted to store energy during operation of the device and discharge upon termination of the electron beam. 